Refrigeration system having a variable speed compressor

Abstract

A two-stage cascade refrigeration system is provided having a first refrigeration stage and a second refrigeration stage. The first refrigeration stage defines a first fluid circuit for circulating a first refrigerant, and has a first compressor, a condenser, and a first expansion device that is in fluid communication with the first fluid circuit. The second refrigeration stage defines a second fluid circuit for circulating a second refrigerant, with the second refrigeration stage having a second compressor, a second expansion device, and an evaporator that is in fluid communication with the second fluid circuit. A heat exchanger is in fluid communication with the first and second fluid circuits to exchange heat between the first and second refrigerants. At least one of the first or second compressors is a variable speed compressor.

1. A two-stage cascade refrigeration system comprising:
 a first refrigeration stage defining a first fluid circuit for circulating a first refrigerant, the first refrigeration stage having a first compressor, a condenser, and a first expansion device in fluid communication with the first fluid circuit; 
 a second refrigeration stage defining a second fluid circuit for circulating a second refrigerant, the second refrigeration stage having a variable speed second compressor, a second expansion device, and an evaporator in fluid communication with the second fluid circuit; 
 a heat exchanger in fluid communication with the first and second fluid circuits to exchange heat between the first and second refrigerants; 
 at least one controller operatively coupled to the first and second compressors for independently controlling operation thereof; and 
 a sensor operatively coupled to the at least one controller, the sensor being configured to sense a temperature of the first refrigerant at an outlet of the heat exchanger and to generate a signal indicative of the sensed temperature to the at least one controller, the at least one controller being operable to vary the speed of the second compressor in response to the signal. 
 
     
     
       2. A two-stage cascade refrigeration system comprising:
 a first refrigeration stage defining a first fluid circuit for circulating a first refrigerant, the first refrigeration stage having a first variable speed compressor, a condenser, and a first expansion device in fluid communication with the first fluid circuit; 
 a second refrigeration stage defining a second fluid circuit for circulating a second refrigerant, the second refrigeration stage having a second variable speed compressor, a second expansion device, and an evaporator in fluid communication with the second fluid circuit; 
 a heat exchanger in fluid communication with the first and second fluid circuits to exchange heat between the first and second refrigerants; 
 a cabinet having an interior and a door providing access into the interior; 
 at least one controller operatively coupled to the first and second variable speed compressors for independently controlling operation thereof; and 
 a sensor operatively coupled to the at least one controller and configured to sense a condition of the door and to generate a signal indicative of the sensed condition to the at least one controller, the at least one controller being operable to vary the speed of at least one of the first or second compressors in response to the signal. 
 
     
     
       3. The two-stage cascade refrigeration system of  claim 2 , wherein the sensor is configured to sense a condition of the door over a predetermined period of time and to generate a signal indicative of the condition of the door over the predetermined period of time to the at least one controller, the at least one controller being operable to vary the speed of at least one of the first or second compressors in response to the signal. 
     
     
       4. A two-stage cascade refrigeration system comprising:
 a first refrigeration stage defining a first fluid circuit for circulating a first refrigerant, the first refrigeration stage having a first compressor, a condenser, and a first expansion device in fluid communication with the first fluid circuit; 
 a second refrigeration stage defining a second fluid circuit for circulating a second refrigerant, the second refrigeration stage having a second compressor, a second expansion device, and an evaporator in fluid communication with the second fluid circuit, at least one of the first or second compressors being a variable speed compressor; 
 a heat exchanger in fluid communication with the first and second fluid circuits to exchange heat between the first and second refrigerants; 
 at least one controller operatively coupled to the first and second compressors for independently controlling operation thereof; and 
 a sensor operatively coupled to the at least one controller and being configured to sense a temperature of ambient air proximate the condenser and to generate a signal to the at least one controller indicative of the sensed temperature, the at least one controller being operable, in response to the signal, to vary the speed of the at least one of the first or second compressors. 
 
     
     
       5. A two-stage cascade refrigeration system comprising:
 a first refrigeration stage defining a first fluid circuit for circulating a first refrigerant, the first refrigeration stage having a first compressor, a condenser, and a first expansion device in fluid communication with the first fluid circuit; 
 a second refrigeration stage defining a second fluid circuit for circulating a second refrigerant, the second refrigeration stage having a second compressor, a second expansion device, and an evaporator in fluid communication with the second fluid circuit, at least one of the first or second compressors being a variable speed compressor; 
 a heat exchanger in fluid communication with the first and second fluid circuits to exchange heat between the first and second refrigerants; 
 at least one controller operatively coupled to the first and second compressors for independently controlling operation thereof; and 
 a sensor operatively coupled to the at least one controller and being configured to sense a temperature of the first refrigerant at an outlet of the heat exchanger and to generate a first signal indicative of the sensed temperature to the at least one controller, the at least one controller being operable to compare the sensed temperature to a predetermined threshold temperature above which the second compressor is not activated by the at least one controller. 
 
     
     
       6. The two-stage cascade refrigeration system of  claim 5 , further comprising:
 a sensor operatively coupled to the at least one controller and being configured to sense the temperature of ambient air proximate the condenser and to generate a second signal indicative of the sensed temperature to the at least one controller, the at least one controller being operable, in response to the second signal, to vary the predetermined threshold temperature above which the second compressor is not activated by the at least one controller. 
 
     
     
       7. The two-stage cascade refrigeration system of  claim 5 , further comprising:
 a cabinet having an interior; and 
 a sensor operatively coupled to the at least one controller and being configured to sense the temperature of the interior of the cabinet and to generate a second signal indicative of the cabinet interior temperature to the at least one controller, the at least one controller being operable, in response to the second signal, to delay activation of the second compressor. 
 
     
     
       8. A method of operating a refrigeration system, comprising:
 circulating a first refrigerant through a first compressor, a condenser, and a first expansion device of a first stage of the refrigeration system; 
 circulating a second refrigerant through a second compressor, a second expansion device, and an evaporator of a second stage of the refrigeration system; 
 exchanging heat between the first and second refrigerants by circulating the first and second refrigerants through a heat exchanger; 
 sensing a temperature of the first refrigerant at an outlet of the heat exchanger; 
 generating a signal indicative of the sensed temperature; and 
 varying the speed of the second compressor in response to the signal to control the flow of the second refrigerant. 
 
     
     
       9. A method of operating a refrigeration system, comprising:
 circulating a first refrigerant through a first compressor, a condenser, and a first expansion device of a first stage of the refrigeration system; 
 circulating a second refrigerant through a second compressor, a second expansion device, and an evaporator of a second stage of the refrigeration system; 
 exchanging heat between the first and second refrigerants; 
 providing a cabinet having an interior cooled by the refrigeration system, the cabinet having a door for accessing the interior of the cabinet; 
 sensing a condition of the door; 
 generating a signal indicative of the sensed condition; and 
 varying the speed of at least one of the first or second compressors in response to the signal to control the flow of at least one of the first or second refrigerants. 
 
     
     
       10. A method of operating a refrigeration system, comprising:
 circulating a first refrigerant through a first compressor, a condenser, and a first expansion device of a first stage of the refrigeration system; 
 circulating a second refrigerant through a second compressor, a second expansion device, and an evaporator of a second stage of the refrigeration system; 
 exchanging heat between the first and second refrigerants; 
 obtaining a cabinet having an interior cooled by the refrigeration system, the cabinet having a door for accessing the interior of the cabinet; 
 sensing a condition of the door over a predetermined period of time; 
 generating a signal indicative of sensed condition of the door over the predetermined period of time; and 
 varying the speed of at least one of the first or second compressors in response to the signal to control the flow of at least one of the first or second refrigerants. 
 
     
     
       11. A method of operating a refrigeration system, comprising:
 circulating a first refrigerant through a first compressor, a condenser, and a first expansion device of a first stage of the refrigeration system; 
 circulating a second refrigerant through a second compressor, a second expansion device, and an evaporator of a second stage of the refrigeration system; 
 exchanging heat between the first and second refrigerants by circulating the first and second refrigerants through a heat exchanger; 
 selectively varying the speed of at least one of the first or second compressors to control the flow at least one of the first or second refrigerants; 
 sensing a temperature of the first refrigerant at an outlet of the heat exchanger; 
 generating a signal indicative of the sensed temperature; and 
 comparing the sensed temperature to a predetermined threshold temperature above which the second compressor is inactive. 
 
     
     
       12. The method of  claim 11 , further comprising:
 sensing a temperature of ambient air proximate the condenser; 
 generating a second signal indicative of the sensed temperature; and 
 varying, in response to the second signal, the predetermined threshold above which the second compressor is inactive. 
 
     
     
       13. The method of  claim 11 , further comprising:
 obtaining a cabinet having an interior cooled by the refrigeration system; 
 sensing a temperature of the interior of the cabinet; 
 generating a second signal indicative of the sensed temperature; and 
 delaying activation of the second compressor in response to the second signal.